The Activation of Protein Kinase C and Protein Kinase D in Human Natural Killer Cells: The Effects of Tributyltin, Dibutyltin, and Tetrabromobisphenol A
Natural killer (NK) cells are lymphocytes that destroy (lyse) tumor cells, virally infected cells, and antibody coated cells. Although past studies have shown that inhibition of protein kinase C (PKC) blocks the lytic function of NK cells, the direct activation of PKC by exposure to lysis sensitive targets had not been examined. To verify that PKC and protein kinase D (PKD) activation occurs as a part of the lytic signaling pathway of NK cells, human NK cells were exposed to target tumor cells for 10 min, 30 min, and 1h. Exposure to K562 tumor cells for both 10 and 30 minutes caused an increase in the phosphorylation (activation) of both PKC and PKD. Previous studies have shown that the compounds tributyltin (TBT), dibutyltin (DBT), and tetrabromobisphenol A (TBBPA) decrease human NK cell lytic function and activate the mitogen activated protein kinase (MAPK) signaling pathway. The current study will examine the effects of DBT, TBT, and TBBPA exposures on the activation of PKC and PKD in human NK cells. NK cells were exposed to 300 - 25 nM TBT, 10 - 0.5 µM DBT, and 10 - 0.5 µM TBBPA for 10 min, 1h, and 6h. Ten minute exposures to 300 - 50 nM TBT activated PKC and to 300 - 100 nM TBT activated PKD; and significantly increased total PKD levels at 25 nM TBT. A 6h exposure to 300 - 25 nM TBT increased P-PKD levels but were not statistically significant. Ten minute exposure to 2.5 µM DBT and one hour exposure to 2.5 µM and 1µM DBT activated PKC. A 10 min exposure to 5 µM DBT activated PKD, and 0.5 µM DBT significantly decreased total PKD levels. The total PKD levels decreased significantly after 6h exposure to 10 and 5 µM TBBPA. P-PKC levels significantly decreased after a 6h exposure to 5 µM TBBPA. These data show for the first time that activation of PKD is part of the lytic signaling pathway of NK cells. Further, they demonstrate that exposure to the contaminants TBT and DBT activates the upstream activator of the lytic pathway, PKC as well as PKD.
"The Activation of Protein Kinase C and Protein Kinase D in Human Natural Killer Cells: The Effects of Tributyltin, Dibutyltin, and Tetrabromobisphenol A"
ETD Collection for Tennessee State University.